Identifying Impairments after Concussion: Normative Data versus Individualized Baselines

SCHMIDT, J. D., J. K. REGISTER-MIHALIK, J. P. MIHALIK, Z. Y. KERR, and K. M. GUSKIEWICZ. Impairments after Concussion: Normative Data versus Individualized Baselines. Med. Sci. Sports Exerc., Vol. 44, No. 9, pp. 1621-1628, 2012. Purpose: This study aimed to determine whether agreement exists between baseline comparison (comparison of postconcussion scores to individualized baseline scores) and normative comparison (comparison of postconcussion scores to a normative mean) in identifying impairments after concussion. Methods: A total of 1060 collegiate student-athletes completed baseline testing as part of an ongoing clinical program. Gender-specific normative means were obtained from a subset of 673 athletes with no history of self-reported concussion, learning disabilities, or attention-deficit disorders. Concussions were later diagnosed in 258 athletes who had completed baseline testing. The athletes completed their first assessment within 10 d after injury. Athletes completed a computerized neurocognitive test (Automated Neuropsychological Assessment Metrics), postural control assessment (Sensory Organization Test), and a 15-item graded symptom checklist at baseline and again after injury. We computed two postconcussion difference scores for each outcome measure: 1) baseline difference = postconcussion score individualized baseline score and 2) normative difference = postconcussion score normative mean. Athletes were considered impaired if postconcussion difference exceeded the reliable change parameters. McNemar tests were used to assess agreement on impairment status (impaired and unimpaired) between comparison methods for each outcome measure. Results: The baseline comparison method identified 2.6 times more impairments than the normative comparison method for the Simple Reaction Time Test I (P = 0.043). The normative comparison method identified 7.6 times more impairments than the baseline comparison method for Mathematical Processing (P < 0.001). No other disagreements were observed for postural control or symptom severity. Conclusions: Our findings suggest that, when using these concussion assessment tools, clinicians may consider using normative data in lieu of individualized baseline measures. This may be especially useful to clinicians with limited resources and an inability to capture valid baselines on all athletes.